Over the past 15 years, there has been an interest in possible associations between fish oil and affective illness, particularly depression. Low plasma levels of docosahexaenoic acid, an essential fatty acid found in fish oil, are associated with low concentrations of cerebrospinal fluid 5-hydroxyindolacetic acid (5-HIAA), a marker of central nervous system serotonin turnover. Epidemiologically, those populations with higher fish oil consumption tend to have lower rates of depression, and reported low levels of fish consumption have been associated with a greater risk of depression in women. It has been hypothesized that omega-3 PUFAs alter brain phospholipid composition and enhance membrane fluidity, and this is supported by evidence that supplementation with omega-3 PUFAs decreases brain water proton transverse relaxation times in patients with bipolar disorder. The association with depression and the proposed mechanism of action elicited some interest regarding associations between omega-3 PUFAs and anxiety disorders. Supplementation trials have shown mixed results, with no effects for obsessive compulsive disorder in patients taking maximum doses of selective serotonin reuptake inhibitors, and another showing decreased anxiety symptoms in 22 patients enrolled in a substance abuse treatment program. Recently, Kiecolt-Glaser and colleagues described a decrease in test-related anxiety symptoms in a non-clinical sample of medical students related to supplementation with omega-3 PUFAs. Although there has been some interest in the use of omega-3 PUFA supplementation as an adjunctive treatment for anorexia nervosa, there have been no systematic trials.